I started investigating this, but unfortunately, one of the root causes of the problem is already hard to solve: The B3DM files in the 1.0 folder of the attached archive indeed contain glTF 1.0. Now your goal was to update that glTF 1.0 file to glTF 2.0, but a deeper problem is that the input file is already invalid: The JSON part of that file contains
"buffers" : {
"KHR_binary_glTF" : {
"byteLength" : 13308
}
},
but the ID of that buffer should not be KHR_binary_glTF, but just binary_glTF (as described in the old specification).
(I even tried to change that, for a single file, manually, with a HEX editor, but that’s difficult, and even if it was a step towards making the file valid, wouldn’t help you much…)
You mentioned that the original data was created with TerraExplorer Pro 7.2. I don’t know the technical details of that software - for example, I do not know if it exports B3DM with glTF 2.0 in the latest version. In any case, the fact that they apparently export invalid glTF 1.0 data in their B3DMs already is a problem. You might consider reaching out to them (or consider a different tool for converting the input data to 3D Tiles, if such a tool is available).